Many industrial systems in operation today have lines or tubes designed to contain only air or other gases. Where a back-flow of liquids into these lines can create harmful conditions, or where such back-flow might indicate an unwanted diversion of expensive or dangerous liquids, means of detecting liquid would be useful. Also, where the lines contain radioactive materials or otherwise hostile environments, it is desirable to detect the presence of a liquid in a line without penetrating the line. Further difficulties are encountered in detecting liquids in small diameter tubes less than 3/8 inches o.d., especially where the liquid backflow may contain entrapped gas.
Techniques for sensing fluid presence in a tube include measuring the conductivity or capacitance of a fluid, or measuring the attenuation of gamma, x-ray, visible or infra-red energy beams passed through a fluid. These techniques require costly equipment which is susceptable to damage, or misalignment, from rough handling. Further, these systems require continuous-wave excitation techniques, which are susceptible to deleterious reflection signals.
It is therefore an object of the present invention to detect the presence of liquid in a small diameter tube without penetrating the tube.
Another object of the present invention is to detect the presence of liquid in a tube without using continuous-wave excitation techniques.
An additional object of the invention is to provide an accurate and reliable liquid detection scheme that may be embodied in durable, relatively inexpensive equipment.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
These and other objects of the present invention are accomplished by providing an arrangement for detecting the presence of liquids in a line, by measuring the liquid-induced change in an ultrasonic signal which is coupled to the line.
Non-intrusive ultrasonic liquid-in-line sensors of the electrical-mechanical transducing type are secured to the outside of the line to be monitored. Short bursts of an ultrasonic signal are transmitted between transducing elements. The first few cycles received are isolated and their amplitude is measured. A reduced amplitude indicates the presence of a liquid in the line. Two transducer arrangements are provided for lines of varying sizes. A first arrangement comprises longitudinally displaced transducing elements bonded to a flat region formed along the outer surface of the line. Another arrangement, especially suited for very small size lines, comprise pairs of sending and receiving transducers bonded to the outside surface of a line. No flats are formed in the line of the second embodiment. The sending transducers are diametrically opposed to each other, as are the pair of receiving transducers. The receiving transducers are rotated 90.degree. with respect to the pair of sending transducers and are axially displaced therefrom. In either arrangement, the tubing walls are operated in a flexural mode, wherein the wall of the line flexes in resonance in response to longitudinal excitation of the drive transducers.